Stable powder coating compositions

Abstract

The invention provides powder coatings that produce consistent finishes when cured, and are stable when uncured. These powder coatings of the invention include novel film forming systems. The novel film forming system, in turn, includes a polymer component and a crosslinker component. In one embodiment, the crosslinker component is novel; and, in another embodiment, both the crosslinker and polymer components are novel. The novel crosslinker component includes a novel, polyfunctional isocyanate compound which is at least partially blocked with at least one of the following: a polyhydroxy aromatic compound, or a mixture of a polyhydroxy aromatic compound and a hydroxy-functional ester compound. The novel polymer component which can be used when practicing certain embodiments of this invention includes a novel polyester polyol. This novel polyester polyol includes the reaction product of a cycloaliphatic component and a polyfunctional isocyanurate component.

That which is:  
     
       1. A powder coating composition comprising a film forming resin system, wherein said film forming resin system comprises: 
       a. a crosslinker component comprising a polyfunctional isocyanate which is at least partially blocked with a mixture of the following:  
       i. a polyhydroxy aromatic compound comprising at least one compound having at least one of the following structures:  
       
         
           HO—Φ 1 —R 1 —Φ 1 —OH  
         
       
       where Φ 1  consists of a phenylene group, and R 1  is an alkylene group having 0 to 4 carbon atoms, or  
       
         
           HO—Φ 2 —OH  
         
       
       where Φ 2  consists of a phenylene group or a naphthylene group, and  
       ii. a hydroxy-functional ester compound having the following structure:  
       
         
           COOR 2 —Φ 2 —OH  
         
       
       where R 2  is an alkyl group having from 1 to 4 carbon atoms, and Φ 2  consists of a phenylene group or a naphthylene group, wherein the ratio of polyhydroxy aromatic compound to the hydroxy-functional ester compound ranges from 0.01:1 to 1.4:1, and  
       b. a polymer component comprising a polyester polyol which comprises a cycloaliphatic component, said cycloaliphatic component comprising the reaction product of:  
       i. a cycloaliphatic acid comprising at least one compound selected from the group consisting of: the 1,2-isomer of hexahydrophthalic acid; the 1,3-isomer of hexahydrophthalic acid; and the 1,4-isomer of hexahydrophthalic acid, and  
       ii. a cyclic polyol comprising at least one compound selected from the group consisting of: cyclohexane dimethanol and cyclohexane diol.  
     
     
       2. A powder coating composition comprising a film forming resin system, wherein said film forming resin system comprises: 
       a. a crosslinker component capable of crosslinking a polymeric polyol, said crosslinker component comprising a polyfunctional isocyanate which is at least partially blocked with a mixture of a polyhydroxy aromatic compound and a hydroxy-functional ester compound, wherein the ratio of polyhydroxy aromatic compound to the hydroxy-functional ester compound ranges from 0.01:1 to 1.4:1, and wherein the polyhydroxy aromatic compound has at least one of the following structures:  
       
         
           HO—Φ 1 —R 1 —Φ 1 —OH  
         
       
       where Φ 1  consists of a phenylene group, and R 1  is an alkylene group having 0 to 4 carbon atoms, or  
       
         
           HO—Φ 2 —OH  
         
       
       where Φ 2  consists of a phenylene group or a naphthylene group, and wherein the hydroxy-functional ester compound has the structure: 
       
         
           COOR 2 —Φ 2 —OH  
         
       
       where R 2  is an alkyl group having 0 to 4 carbon atoms and Φ 2  consists of a phenylene group or a naphthylene group; and 
       b. a polymeric polyol component comprising a polyester polyol, said polyester polyol comprising a cycloaliphatic component, wherein the cycloaliphatic component comprises the reaction product of:  
       i. a cycloaliphatic acid, and  
       ii. a cyclic polyol.  
     
     
       3. The powder coating composition recited in claim  2 , wherein the cycloaliphatic acid comprises at least one compound selected from the group consisting of: the 1,2-isomer of hexahydrophthalic acid; the 1,3-isomer of hexahydrophthalic acid; and the 1,4-isomer of hexahydrophthalic acid. 
     
     
       4. The powder coating composition recited in claim  2 , wherein the cycloaliphatic acid comprises hexahydrophthalic anhydride. 
     
     
       5. The powder coating composition recited in claim  2 , wherein the amount of the cycloaliphatic acid employed is at least about 40 weight percent, said weight percentage being based upon the total weight of the polyester polyol. 
     
     
       6. The powder coating composition recited in claim  2 , wherein the amount of the cycloaliphatic acid employed is at most about 55 weight percent, said weight percentage being based upon the total weight of the polyester polyol. 
     
     
       7. The powder coating composition recited in claim  2 , wherein the cyclic polyol comprises at least one compound selected from the group consisting of: cyclohexane dimethanol and cyclohexane diol. 
     
     
       8. The powder coating composition recited in claim  2 , wherein the amount of the cyclic polyol employed is at least about 10 weight percent, said weight percentage being based upon the total weight of the polyester polyol. 
     
     
       9. The powder coating composition recited in claim  2 , wherein the amount of the cyclic polyol employed is at most about 70 weight percent, said weight percentage being based upon the total weight of the polyester polyol. 
     
     
       10. The powder coating composition recited in claim  2 , wherein the amount of the cycloaliphatic component employed is at least about 60 weight percent, said weight percentage being based upon the total weight of the polyester polyol. 
     
     
       11. The powder coating composition recited in claim  2 , wherein the amount of the cycloaliphatic component employed is at most about 99 weight percent, said weight percentage being based upon the total weight of the polyester polyol.